In the first, the condition is now more important than how to meet it. (At least in my perception. In the latter two, I just switched and personally think it is clearer that way. Note that English is not my native tongue and that I am very well aware that not all people think alike. That is why I love perl5: it is very easy to write it as it best fits your mind while still not too hard to read when others wrote it the way they think is best.

In the third example it is also important to realize the number of options on either side of the and/or/if/unless.

If it is too hot, turn down the heating
If it is too hot, open the window
If it is too hot, turn on the air conditioning
If it is too hot, go out for some fresh air